1. Field of the Invention
This invention relates to a method for manufacturing a stent for treating internal tubular organs such as a blood vessel and more particularly for treating aneurysm.
2. Description of Related Art
Inside a body, there are many tubular organs, such as a blood vessel, a bile duct, a ureter, an esophagus, or the like; such organs bear a possibility of characteristic ailments such as stenosis or occlusion. For example, in respect of blood vessels, there are possibilities of ailments such as stenosis, occlusion, aneurysm, varicosity, and the like. More particularly, since aneurysm is a serious ailment where a rupture of a blood vessel causes excessive bleeding, prompt treatment is to be required, and various tools have been developed for treating thus ailment effectively.
Lately, the use of a metallic cylindrical tool called a stent is increasingly used for treating a portion of blood vessel stenosis or for treating aneurysm. For example, when treating aneurysm, a stentgraf, which covers the stent with an artificial blood vessel, is used; such stentgraf is positioned in place at the inner side of the aneurysm so that pressure of blood would not affect the aneurysm.
As for examples regarding the kinds of stents, there is a cylindrical stent made from a metal material (representatively from stainless steel) or a stent having a metal wire bent in a zigzag manner while at the same time having a cylindrical shape. Such stents are delivered to an affected portion internally through a blood vessel and positioned in place when reaching the affected portion.
In a case of positioning the stent at the affected portion, the stent is diametrally shrunk and confined within a long tubular delivery kit, in which the delivery kit has a guiding wire inserted therethrough; and then, starting from the guiding wire, the delivery kit is guided through a blood vessel from a portion such as the root of a leg till reaching the affected portion, and then, when reaching the affected portion, the delivery kit is retracted to release the stent from confinement. After being released from confinement, the stent diametrally self-expands, and is positioned in place at the affected portion in thus expanded state for protecting the blood vessel.
When the stent is released from confinement as mentioned above, it would be necessary for the stent to precisely return back to the original diameter (diameter before diametral shrinkage). If the return back to the original diameter lacks precision, preparation of a stent with a diameter anticipating the rate of returning back would become necessary and would cause the requirement of extra labor and material.
Meanwhile, as for zigzag shaped stents, various shapes thereof have been proposed as shown in FIG. 5. A stent 51 shown in FIG. 5(a) is structured having numerous short members 51 a welded at the end portions thereof. Although the stent 51 has a characteristic of being easily diametrally shrunk, the material for the member 51a will be limited owing to the requirement of a welding procedure. A stent 52 shown in FIG. 5(b) is structured with a single wire having a relatively large bending radius. Although the stent 52 has a characteristic of being resistant to fracture owing to a low degree of processing, the stent 52 has a difficulty of being diametrally shrunk, A stent 53 shown in FIG. 5(c) is structured with a single wire having a relatively small bending radius. Although the stent 53 has a characteristic of being easily diametrally shrunk, thc stent has a problem of being easily fractured owing to a high degree of processing.
Although stainless steel is typically used as a material for the stent as mentioned above, a stainless steel stent raises a problem of not being able to sufficiently return back to the original diameter after being released from confinement, in a case when the elasticity limit for stainless steel is exceeded during diametral shrinkage.
Accordingly, it is preferable for a shape-memorizing alloy of Nickel (Ni) and Titanium (Ti) to be used as the material for the stent instead of stainless steel, since the alloy is: durable against repetitive force when in a range exceeding elasticity; corrosion-resistant; and safe upon the living body.
However, when attempting to manufacture the foregoing zigzag shaped stents 51 through 53 with use of a shape-memorizing alloy comprised of Nickel and Titanium, the stent 51 could not be applied upon, owing to the requirement of welding. Further, in respect of the stent 52, owing to the large bending radius, a wire diameter could be thickened to allow high rigidity; nevertheless, containment into the delivery kit would be difficult since diametral shrinkage is difficult to be performed. Further, in respect of the stent 53, owing to the high diametral shrinkage ability of the stent 53, containment into the delivery kit could be performed easily, nevertheless, reduction of a bending radius during a bend-processing would heighten the degree of processing to raise the possibility of causing fracture.
Due to the foregoing problems, conventionally, it was difficult to manufacture a zigzag shaped stent using a wire made from a shape memorizing alloy of Nickel and Titanium which could satisfy the conditions of being able to diametrally shrink with ease and being difficult to become fractured.
It is an objet of this invention to provide a method of manufacturing a stent using a shape-memorizing alloy comprised of Nickel and Titanium, in which the stent is capable of reducing a bending radius and is therefore capable or enabling sufficient diametral shrinkage.
The present inventor has attempted various experiments for developing a method of manufacturing a stent by bend-processing a wire made from a shape-memorizing alloy of Nickel and Titanium. As a result, it has been found that the possibility of fracture during a process of bending the wire made from the Nixe2x80x94Ti alloy depends on the difference in the past history of the wire.
An experiment have been performed where wires of equal thickness are bent into a same radius, in which one wire is made of a material being shape-memorized with a straight line shape, and the other wire is made of a material not having been shape-memorized. The experiment has tested whether or not fracture will occur during a process of detaching the wires from a jig and returning the wires back to the straight line shape after the wires have been shape-memorized into respective bending radiuses, under the conditions that: the datum for each item is 5; the bending radius ranges from 0.1 mm through 0.6 mm; and the thickness of the wire are respectively 0.3 mm, 0.4 mm, 0.5 mm. Thc result for the experiment is shown in chart 1. In chart 1, an X mark is applied when there is one or more fractured wires within datum 5, and a circle mark is applied when all of five are not fractured.
As the results shown in chart 1, the wire already having been shape-memorized is more likely to fracture at a level of a larger radius compared to the wire not having been subject to shape-memorization.
Accordingly, the method of manufacturing a stent regarding this invention is a method of manufacturing a zigzag shaped stent made from a shape-memorizing alloy comprised of nickel and titanium, wherein the method serves to perform shape-memorization of a zigzag shape by using a shape-memorizing alloy made wire not having been subject to shape-memorization.
With this method of manufacturing a stent, a process of bending into a small radius could be achieved for enabling memorization of the bent shape by using a wire made from a shape-memorizing alloy of Nickel and Titanium (Nixe2x80x94Ti). Accordingly, a zigzag shaped stent with a small bending radius could be reasonably manufactured without fracture.
Another method of manufacturing a stent regarding this invention is a method of manufacturing a zigzag shaped stent made from a shape-memorizing alloy comprised of nickel and titanium, comprising the steps of: performing a zigzag shape-memorization process in which a shape-memorizing alloy wire not having been subject to shape-memorization is fixed upon a jig in a zigzagging manner; and performing a cylindrical shape-memorization process in which the shape-memorizing alloy wire having been subject to the zigzag shape-memorization is fixed to a cylindrical jig in a wrapping manner.
With this method of manufacturing a stent, a process of bending into a small radius could be achieved for enabling memorization of the bent shape by using a wire made from a shape-memorizing alloy of Nickel and Titanium (Nixe2x80x94Ti); and also enable the wire having memorized the bent shape to further memorize a cylindrical shape. Accordingly, a cylindrical shaped stent with a small bending radius could be reasonably manufactured.